The alkyl phenols are very useful intermediates in the production of plastics, industrial chemicals, pharmaceuticals, and agricultural chemicals. When alkylphenols are obtained from tar acid or by other synthetic methods, their physical properties of their isomers and homologs resemble closely one another. It is, therefore, disadvantageous to isolate industrially each alkylphenol in a pure state from complicated mixtures such as tar acid which contains a large variety of isomers and homologs. On the other hand, synthetic methods such as the sulfonation-alkali fusion process or the cumene process have also some disadvantages. The former produces many isomers and industrial wastes, and the latter requires a large cost of equipment and is accompanied by many side reactions.
Conversion of carbonyl compounds to esters or carboxylic acids is accomplished generally by Baeyer-Villiger oxidation by the use of a per acid or hydrogen peroxide as oxidizing agents. The per acid is used in the presence of acid catalyst and hydrogen peroxide is used in alkaline medium. Both of these agents are, however, practically inadequate to use, since the per acid is rather expensive and reacts slowly, and hydrogen peroxide reacts less selectively. Moreover, the Baeyer-Villigar reaction does not always give a good yield of phenol esters from aromatic aldehydes, owing to its tendency to be oxidized to carboxylic acids (cf., Japanese published patent application Ser. No. 48-56635). To overcome these disadvantages of hitherto used methods, we have carried out various studies on the synthesis of alkylphenol esters which are readily hydrolyzed to alkylphenols by oxidizing the aromatic aldehydes, and found that alkylphenol esters could be synthesized readily and selectively by oxidizing the aldehydes with hydrogen peroxide in the presence of hydrogen fluoride.